Method and apparatus for optimizing latent capacity of a variable speed compressor system

Abstract

An HVAC system includes an evaporator coil and a metering device fluidly coupled to the evaporator coil. The HVAC system also includes a variable-speed circulation fan and a condenser coil fluidly coupled to the metering device. The HVAC system also includes a variable-speed compressor fluidly coupled to the condenser coil and the evaporator coil and a controller operatively coupled to the variable-speed compressor and the variable-speed circulation fan. The controller is configured to measure a speed of the variable-speed compressor, calculate a normal cooling Cubic Feet per Minute (CFM), measure a speed of the variable-speed circulation fan, and determine if the speed of the variable-speed circulation fan exceeds the normal cooling CFM. If the speed of the variable-speed circulation fan exceeds the normal cooling CFM, the HVAC controller adjusts a speed of at least one of the variable-speed compressor and the variable-speed circulation fan.

What is claimed is: 
     
       1. A heating, ventilation, and air conditioning (HVAC) system comprising:
 an evaporator coil; 
 a metering device fluidly coupled to the evaporator coil; 
 a variable-speed circulation fan for circulating air around the evaporator coil; 
 a condenser coil fluidly coupled to the metering device; 
 a variable-speed compressor fluidly coupled to the condenser coil and the evaporator coil; 
 a controller operatively coupled to the variable-speed compressor and the variable-speed circulation fan; and 
 wherein the controller is configured to:
 measure a speed of the variable-speed compressor; 
 calculate a normal cooling Cubic Feet per Minute (CFM); 
 measure a speed of the variable-speed circulation fan; 
 determine if the speed of the variable-speed circulation fan exceeds the normal cooling CFM; 
 responsive to a determination that the speed of the variable-speed circulation fan exceeds the normal cooling CFM, determine if the variable-speed circulation fan is operating at a minimum operating speed below which the variable-speed circulation fan becomes unstable; and 
 responsive to a determination that the variable-speed circulation fan is operating at the minimum operating speed, increase a speed of the variable-speed compressor. 
 
 
     
     
       2. The HVAC system of  claim 1 , wherein the HVAC system is a package HVAC system. 
     
     
       3. The HVAC system of  claim 1 , wherein the HVAC system is a split HVAC system. 
     
     
       4. The HVAC system of  claim 1 , wherein the controller measures the speed of the variable-speed compressor and the variable-speed circulation fan at periodic time intervals. 
     
     
       5. The HVAC system of  claim 4 , wherein the periodic time intervals comprise approximately five seconds. 
     
     
       6. The HVAC system of  claim 1 , wherein responsive to the determination that the variable-speed circulation fan is not operating at the minimum operating speed, the controller is configured to lower a speed of the variable-speed circulation fan. 
     
     
       7. The HVAC system of  claim 6 , wherein maintaining the speed of the variable-speed circulation fan below the normal cooling CFM optimizes the latent capacity of the HVAC system. 
     
     
       8. The HVAC system of  claim 1 , wherein raising the speed of the variable-speed compressor raises the normal cooling CFM. 
     
     
       9. A method of optimizing latent capacity of an HVAC system, the method comprising:
 measuring, using a controller, a speed of a variable-speed compressor; 
 calculating, using the controller, a normal cooling CFM from the measured speed of the variable-speed compressor; 
 measuring, using the controller, a speed of a variable-speed circulation fan; 
 determining if the speed of the variable-speed circulation fan exceeds the normal cooling CFM; 
 responsive to a determination that a speed of the variable-speed circulation fan exceeds the normal cooling CFM, determining if the variable-speed circulation fan is operating at a minimum operating speed below which the variable-speed circulation fan becomes unstable; and 
 responsive to a determination that the variable-speed circulation fan is operating at the minimum operating speed, increasing, using the controller, a speed of the variable-speed compressor. 
 
     
     
       10. The method of  claim 9 , comprising responsive to a determination that the variable-speed circulation fan is not operating at the minimum operating speed, lowering, using the controller, the speed of the variable-speed circulation fan. 
     
     
       11. The method of  claim 9 , comprising measuring the speed of the variable-speed compressor and the speed of the variable-speed circulation fan at periodic time intervals. 
     
     
       12. The method of  claim 11 , wherein the periodic time intervals comprise approximately five seconds. 
     
     
       13. The method of  claim 9 , comprising measuring the speed of the variable-speed compressor and the speed of the variable-speed circulation fan continuously. 
     
     
       14. The method of  claim 9 , comprising optimizing the latent capacity of the HVAC system. 
     
     
       15. A heating, ventilation, and air conditioning (HVAC) system comprising:
 an evaporator coil; 
 a metering device fluidly coupled to the evaporator coil; 
 a variable-speed circulation fan for circulating air around the evaporator coil; 
 a condenser coil fluidly coupled to the metering device; 
 a variable-speed compressor fluidly coupled to the condenser coil and the evaporator coil; 
 a controller operatively coupled to the variable-speed compressor and the variable-speed circulation fan; and 
 wherein the controller is configured to:
 measure a speed of the variable-speed compressor; 
 calculate a normal cooling CFM; 
 measure a speed of the variable-speed circulation fan; 
 determine if the speed of the variable-speed circulation fan exceeds the normal cooling CFM; 
 responsive to a determination that the speed of the variable-speed circulation fan exceeds the normal cooling CFM, determine if the variable-speed circulation fan is operating at a minimum operating speed below which the variable-speed circulation fan becomes unstable; and 
 responsive to a determination that the variable-speed circulation fan is operating at the minimum operating speed, increase a speed of the variable-speed compressor.